Radio object-locating system



Feb. 5, 1952 P. SPENCER 2,584,509

RADIO OBJECT-LOCATING SYSTEM Filed Jan. 22, 1949 DUPLEXING CIRCUIT Z6 y2 8 2 MIX E I? VOLTAGE Z 9 SOURCE H 1 1 1- Z2 AMPLIFIER /2 2/ SWITCH y 0VOLTAGE DETECTOR sou/2C5 4 v F1/, 17 32, A

SWEEP SWITCH KEVER GENERATOR DICAT I'NVENTOI? Psrzcv L. Spa-weer:

' aiented RADIO OBJECT-LOCATING SYSTEM Percy L. Spencer, West Newton,Mass., asslgnor to Raytheon Manufacturing Company, Newton, Mass., acorporation of Delaware Application January 22, 1949, Serial No. 72,167

5 Claims.

This invention relates to radio object-locating systems, for example, ofthe so-called pulse-echo type, operating in the microwave region of theelectromagnetic spectrum.

In systems of the general character above referred to, exploratorypulses of electromagnetic energy are periodically radiated into space,generally at an audio-frequency rate, and upon such energy encounteringan object in said space, a portion thereof suffers reflection. Thereflected energy, known as an echo, is received back at the site of thetransmitting installation and the time intervening between the originaltransmission and the reception of the echo thereof is utilized todetermine the distance to the reflecting object.

The transmitter and receiver usually share a common antenna, means,known as a duplexing circuit, being provided to protect the receiverfrom the high power of the transmitter during the transmitting periods.The receiver is usually of the superheterodyned type and includes alocal oscillator for generating oscillations, preferably,

of a frequency higher than that of the trans-' mitted energy, whichoscillations are mixed in a first detector with the incoming echosignals to derive an intermediate-frequency signal. The latter, afteramplification, is demodulated in a second detector, and the resultingpulses are applied to an indicator, such as a cathode-ray tube, to whichthere is also applied, in synchronism with the pulse transmission, atiming wave, all in a manner well known to those skilled in the art towhich the present invention relates.

A system such as has been described possesses certain disadvantages. Itnecessitates the incorporation of a separate local oscillator, whichadds to the cost thereof. In addition, the local oscillator must haveits frequency maintained at a proper point with respect to the frequencyof the transmitter in order that the intermediatefrequency amplifier,which is ordinarily of the fixed tuned type, accept the signal fedthereto from the first detector. The attainment of this conditionrequires the use of costly frequency stabilizing apparatus.

It is, therefore, among the objects of the present invention to providea radio object-locating system which avoids the necessity for a separatelocal oscillator, thereby materially reducing the cost of the system asa whole.

It is a further object of the present invention to provide a radioobject-locating system which utilizes the source of the exploratoryenergy itself as a local oscillator, whereby costly frequencystabilizingcircuits are eliminated and any tendency of said source to drift infrequency has no effect upon the intermediate-frequency signal developedin the receiver.

These, and other objects of the present invention, which will becomemore apparent as the detailed description thereof progresses, areattained, briefly, in the following manner.

Suitable means for generating electromagnetic energy in the microwaveregion of the spectrum, for example, a magnetron oscillator, is coupled,through a duplexing circuit, to an appropriate microwave antenna system.This oscillator is provided with means for controlling the frequency ofthe energy generated thereby. Suitable potentials are applied to theoscillator and the frequency-controlling means thereof to energize saidoscillator into operation at a predetermined, relatively high frequencyand relatively low power level. The oscillations thus generated areapplied, also through the duplexing circuit, to the first detector ofthe receiver and constitute local oscillator energy for combination withincoming echo signals to derive an intermediatefrequency signal.Periodically, other suitable potentials are applied to the oscillatorand to the frequency-controlling circuit thereof to pulse saidoscillator into operation at a difierent, relatively lower frequency anda relatively high power level.

The oscillations thus generated constitute the exploratory pulses whichare radiated into space and prevented by the duplexing circuit fromentering the receiver.

Thus, between the radiated exploratory pulses, the first detector issupplied with local oscillations which, upon mixing with the receivedecho signals, result in an intermediate-frequency signal which is ofconstant frequency regardless of any drift in the oscillator frequency.

In the accompanying specification there shall be described, and in theannexed drawing shown, an illustrative embodiment of the radioobjectlocating system of the present invention. It is, however, to beclearly understood that the present invention is not to be limited tothe details herein shown and described for purposes of illustrationonly, inasmuch as changes therein may be made without the exercise ofinvention, and within the true spirit and scope of the claims heretoappended.

In said drawing, the single figure is a block diagram of a radioobject-locating system assembled in accordance with the principles ofthe present invention.

Referring now more in detail to the aforesaid illustrative embodiment ofthe present invention,

with particular reference to the drawing illustrating the same, thenumeral Ill schematically designates a microwave oscillator, forexample. of themultiple-cavity magnetron type.

Such an oscillator may include a centrally disposed cathode llsurrounded by a cylindrical anode body l2 which is provided with aplurality of interiorly-extending, radially-disposed anode arms l3, eachpair of adjacent arms, together with those portions of said cylindricalanode body lying therebetween, constituting a cavity resonator. Means(not shown in the interest of simplicity) are conventionally provided toestablish a magnetic field in the interelectrode space of the device,said field extending in a direction transverse to the electron pathbetween the catnode I I and anode arms l3. When the cathode of such adevice is caused to become electron emls sive, as by appropriatelyheating the same by an electric current, and a suitable potentialdiffer-- ence is established between said cathode and the anode, such adevice generates electrical cscib lations in the cavity resonatorsthereof, the frequency of said oscillations being determined, primarily,by the geometry of the physical elements making up such cavityresonators.

It has been found that the natural resonant frequency of such a devicecan be altered by injecting electrons into the cavity resonatorsthereof, particularly, in the high capacitance regions of suchresonators, said electrons altering the dielectric constant of saidresonators, and hence, the capacitance thereof, thereby altering thefrequency of oscillation. In order to accomplish this frequencydeviation, the device may be provided at the opposite open ends of thecavitv resonators with a pair of annular electrodes l4 and I5, one ofsaid electrodes, for example, the electrode M, being thermionicallyemissive, and the remaining electrode constituting an electronreflectingelement. These electrodes are maintained at a suitable negativepotential with respect to the anode body I 2 whereby the electronsemitted by the electrode M are accelerated toward said anode body, manyof them passing downwardly through the cavity resonators and comingunder the influence of the field between the refl cting electrode l 5and the anode body l2. The reflecting electrode l5 causes theseelectrons to move back through the cavity resonators toward the primaryemitting electrode M by which they are again reflected. Some of theelectrons which approach the reflecting electrode l5 have sufficientvelocity to bombard said electrode and bring about secondary electronemission therefrom. In any event, a particular potential differencebetween the electrodes 14 and l5 and the anode body l2 provides acertain electron population in the cavity resonators and thereby fixesthe operating frequency of the device. Alternation of this potentialdifference alters said electron population and changes said operatingfrequency. Thus, the device can be frequency modulated by control of thevoltage applied between $7112 electrodes I4 and i5 and the anode bodyl2.

For a more complete description of a frequency-modulated magnetron, suchas has been briefly described above, attention is directed to anapplication of William C. Brown, Serial No. 655,445, filed March 19,1946, Patent No. 2,556,747, granted June 12, 1951, entitled ElectronDischarge Device.

In the system of the present invention a voltage source IB is providedhaving a relatively low positive voltage output V1 and a relatively highpositive voltage output V2. The negative terminal of this voltage sourceis connected by a conductor I! to the cathode ll of the magnetron l0,and one or the other of the positive potentials Vi'or V2 is applied,through a suitable switch l8 and a conductor Hi, to the anode body l2 ofsaid magnetron. The switch I8 may be under the control of a keyer 20such as is usually employed for triggering the oscillator and thecathode-ray tube timing-wave generator of a conventional pulse-echoradar system.

In the system of the present invention, there is also provided a secondvoltage source 2| having a relatively low negative voltage output V3 anda relatively high negative voltage output V4. The positive terminal ofthis voltage source is connected by a conductor 22 to the anode body l2of the magnetron l0, and one or the other of the negative potentials V3or V4 is applied, through a suitable switch 23 and conductors 24 and 25,to the emitting and reflecting electrodes l4 and 15. The switch 23 maybe similar to the switch 18 and, preferably, is also under the controlof the keyer 20.

The switching, arrangement is preferably such that when the relativelylow positive voltage V: is being applied between the cathode II andanode body !2 of the magnetron, the relatively low negative voltage V3is being applied between the electrodes l4 and I5 and said anode body[2. Under these conditions, the magnetron oscillates at a relatively lowpower level and, because the electron population in the cavityresonators is relatively rare, at a relatively high frequency. If nowthe relatively high positive voltage V2 and the relatively high negativevoltage V4 are connected, respectively, to the cathode-anode circuitll-|2 and the electrode-anode circuit I4--l5-I2, the magnetron willoscillate at a relatively high power level and, because the electronpopulation in the cavity resonators is relatively dense, at a relativelylower frequency.

The output of the magnetron is applied, through a suitable duplexingcircuit 26, to a microwave antenna system 21 and to a first detector ormixer 28, the arrangement being such that when the magnetron isoperating at its relatively low power level and its relatively highfrequency, the duplexing circuit does not break down and most of thegenerated energy is applied to the mixer, but when the magnetron ispulsed into operation at its relatively high power level and itsrelatively lower frequency, said duplexing circuit does break down, theinput to the mixer becomes substantially short-circuited, and most ofthe generated energy is applied to the antenna system 2! for radiationinto space.

As stated in earlier portions of this specification, when theexploratory pulses thus projected into space encounter a reflectinobject, a portion of the energy thereof is reflected and eventuallyreceived by the antenna system 21. During the receiving periodsintervening the exploratory pulses, the mixer 28 is being supplied withthe relatively low power, relatively high-frequency output of themagnetron, and when this energy combines with the received echo signalsin said mixer 28, an intermediate-frequency signal is obtained, thefrequency of which is, preferably, the difference between the twofrequencies generated by the magnetron as above described. Theintermediate-frequency signal is applied to an amplifler 29 and theoutput of the latter is demodulated in a second detector 30. The pulsesthus obtained are applied to an indicator 3| which may be a cathode-raytube of the A-scope, planposition-indicating, many other type. Theindicator 3| may be provided with a suitable timing wave by a sweepvoltage generator 32 operating under the control of the keyer insynchronism with the pulsing of the magnetron ID.

This completes the description of the aforesaid illustrative embodimentof the present invention. It will be noted from all of the forego ingthat there has been provided a pulse-echo radar system in which a singlesource of oscillating energy is utilized to produce the radiatedexploratory pulses, and the local oscillations for developing theintermediate-frequency signal in the receiver, thereby eliminating thenecessity for a separate local oscillator, reducing the cost of thesystem as a whole, and avoiding the frequency-stabilizing circuitsgenerally required in systems having separate local oscillators.

Other objects and advantages of the present invention will readily occurto those skilled in the art to which the same relates.

What is claimed is: e

1. A transmitter for a radio object-locatin system comprising: anoscillator adapted to generate electromagnetic energy; means forcontrolling the frequency of the energy adapted to be generated by saidoscillator; a plurality of voltage sources of different magnitudes;means for conmeeting some of said voltage sources to said oscillator andsaid frequency-controlling means to energize said oscillator intooperation at a predetermined frequency and a predetermined power level;and means for connecting others of said voltage sources to saidoscillator and said frequency-controlling means to energize the sameinto operation at a different frequency and a different power level.

2. A transmitter for a radio object-locating system comprising: anoscillator adapted to generate electromagnetic energy; means forcontrolling the frequency of the energy adapted to be generated by saidoscillator; a plurality of relatively low and relatively high voltagesources; means for connecting said relatively low voltage sources tosaid oscillator and said frequency-controlling means to energize saidoscillator into operation at a relatively high frequency and arelatively low power level; and means for connecting said relativelyhigh voltage sources to said oscillator and said frequency-controllingmeans to energize the same into operation at a relatively low frequencyand a relatively high power level.

3. A radio object-locating system comprising: an oscillator adapted togenerate electromagnetic energy; means for controlling the frequency ofthe energy adapted to be generated by said oscillator; a plurality ofvoltage sources of different magnitudes; means for connecting some ofsaid voltage sources to said oscillator and said frequency-controllingmeans to energize said oscillator into operation at a predeterminedfrequency and a. predetermined power level; means for connecting othersof said-voltage sources to means, and at another of said frequencies andpower levels to said detector.

4. A radio object-locating system comprising: an oscillator adapted togenerate electromagnetic energy; means for controlling the frequency ofthe energy adapted to be generated by said oscillator; a plurality ofrelatively low and relatively high voltage sources; means for connectingsaid relatively low voltage sources to said oscillator and saidfrequency-controlling means to energize said oscillator into operationat a relatively high frequency and a relatively low power level; meansfor connecting said relatively high voltage sources to said oscillatorand said frequency-controlling means to energize the same into operationat a relatively low frequency and a relatively high power level; saidtwo last-named means being alternately operable; means for radiatingelectromagnetic energy into space and receiving portions thereofreflected from objects to be located therein; a beat-frequency detector;and means, coupled to said oscillator, said radiating-receiving means,and said detector, for directing the major portion of the energygenerated at the lower frequency and higher power level to saidradiatingreceiving means, and at the higher frequency and lower powerlevel to said detector.

5. A transmitter for a radio object-locating system comprising: amagnetron oscillator of the cavity resonator type; means for energizingsaid oscillator to generate electromagnetic energy of predeterminedpower; electronic tuning means for adjusting the frequency of the energythus generated; and means coupled to said energizing and tuning meansfor controlling the same to simultaneously alter the power level andfrequency of said energy.

PERCY L. SPENCER.

REFERENQSS CITED The following references are of record in the file ofthis patent:

UNITED STATES RATENTS Number Name Date 2,423,024 Hershberger June 24,1947 2,424,854 Sanders July 29, 1947 2,427,191 Brink Sept. 9, v19472,433,669 Keister Dec. 30, 1947 2,444,388 De Vries June 29, 19482,451,141 Wolfl Oct. 12, 1948 2,523,684 Dow Sept. 26, 1950

